Choosing organic compost, insecticide & fertiliser

Val Bourne

Find out which organic insecticides, composts, fertilisers and plant feeds to use in your garden.

Choosing the right natural fertiliser

Fertilisers major on three ingredients and they are always listed in this order.

  • Nitrogen (N) - encourages foliage
  • Phosphorus (P) - encourages rooting and flower buds
  • Potassium (K) - ensures plant vigour and health

Different fertilisers contain different ratios of the three major ingredients recorded as a series of a numbers. 5-10-5 is twice as rich in phosphorous as it in nitrogen and potassium.

Related: how to improve your soil.

Slow release versus fast release

Some fertilisers release their nutrients quickly while others are much slower. For the gardener, the slow- to medium-release balanced fertilisers with equal amounts of the three major ingredients are best for general use. They do not promote a surge of fast sappy growth but they do encourage general growth and vigour. Nitrogen-rich feeds promote leaf at the expense of flower.

Blood, fish and bone (usually recorded as 5-5-6.5)

  • A balance of nitrogen, phosphorus and potassium to boost all-round fertility.
  • Easy to store and handle.
  • Good for adding to the ground to raise fertility, or increase soil nutrients following a hungry crop like potatoes.
  • Does not affect flower and fruiting as nitrogenous feeds can do.

Dried chicken manure (4-3.5-2)

  • Pelleted forms and powdered forms.
  • Easy to store and handle - but smells.
  • Easy to apply.
  • Rich in nitrogen and lower in potassium - so good for feeding hellebores or promoting leafy crops.

Liquid seaweed (ratios vary)

  • Concentrated liquid that needs diluting.
  • Easy to water on to seedlings and releases nutrients slowly.
  • High in potash but needs continual applications to improve growing conditions.
  • Variable product.

Choosing your ready-made fertiliser

Tomatoes, strawberries and bedding plants need a phosphorous-rich feed to encourage flowers, such as Tomarite.

Brassicas tend to be given a nitrogen-rich fertiliser to promote leafy growth.

Garden compost

This is often low in nutrients although well-balanced otherwise. The bacteria involved keep nitrogen low. But this organic material improves soil structure when dug in, creating a friable mixture that encourages root growth.

The process of adding green waste to your own heap is very eco-friendly and, added over many years, it will improve your soil.

If you have a preponderance of grass clippings lay them on a sheet for 24 hours in a sunny place and either add them to your heap (once brown) or mulch raspberries etc.

Related: how to make a compost heap.

Nettle and comfrey tea

Certain leaves left to rot in water form a nutritious liquid - although the process smells rather evil. Nettles' water can be tipped onto potatoes etc.

Comfrey Tea is more refined and it’s possible to make a wall-mounted comfrey tea maker using a drainpipe sealed at both ends with removable pieces. Feed the leaves into the top and drain the brown tea from the base after two to three weeks. Dilute before using one part tea to twenty parts water. Garden Organic have instructions on their website -

Chopped comfrey leaves can also be used as an accelerator on the compost heap and put into potato trenches, so planting Comfrey Bocking 14 by a compost heap is an excellent idea and the flowers are rich in nectar.

Related: how to make comfrey tea.

Letting nature take care of pests

Everybody’s garden should contain a rich ecosystem of interacting processes, which I refer to as a living jigsaw in my book The Natural Gardener. There are no good and bad guys in the natural world.

The ladybird needs a diet of aphids to survive and will only lay clusters of eggs close to aphid colonies. If you have no aphids you won’t attract ladybirds. Therefore it is not a good idea to target aphids and other pests with a chemical. This includes soft soap and so-called 'green' mustard-based sprays.

The spraying problem is exacerbated by the disparity of life cycles between predator and pest. The seven-spot ladybird produces one generation per year, although her 1500 eggs are laid in batches of 30, between May and August typically. 

The aphid has the ability to produce 40 generations in one year - often asexually. Mustard sprays or insecticides will kill both and many more insects, allowing the aphids to bounce back and breed unchecked by predators.

Aphids target specific plants and will soon be attacked by birds, parasitic wasps, hoverfly larva and other predatory creatures.

If aphids are really troubling you simply squeeze them through your fingers or wash them off with ordinary water. Don’t even add washing up liquid.

Improving your garden's eco system

Improving your garden's eco system is the key to not having to rely on chemical fertilisers or pesticides.

1. Plant diversely using some trees, shrubs, perennials, grasses, bulbs, annuals - this will pull in more insect and animal life.

2. Put plants in their correct positions so that they remain healthy and avoid stress which eventually leads to disease. Making sure, for instance, that sun-loving Mediterranean plants have full sun and good drainage.

3. Grow the plants that match your conditions. Don’t aspire to garden phlox if you have thin, poor soil: it will always succumb to mildew. Go for plants that enjoy poorer soil - like eryngiums, pinks, verbascums and poppies.

4. Plant densely to create cover as this provides shelter for beetles and other helpful insects.

5. Leave some areas undisturbed - under shrubs and in corners so that bumble bees have somewhere to nest. These areas will also attract hibernating toads, frogs, hedgehogs and newts.

6. Long grass should feature in every garden where possible. It can be stylishly done - just cut a path through the grassy swathe. The National Trust have found that not mowing encourages brown butterflies to breed, shelters amphibians and allows wild flowers to return.

7. Have a range of plants that flower from early in the year until late in the year - to ensure a supply of nectar. Early-flowering plants are particularly important for solitary and bumble bees emerging from hibernation. Late-flowering plants are also important and cosmos and gaura are two plants often still in flower in November. Nectar strength varies from plant to plant. Some fritillaria nectar contains only 4%, but origanum nectar contains a staggering 68% of sugar. Not surprisingly the garden form O. laevigatum 'Herrenhausen' attracts droves of bees and butterflies in August. Spotted and veined flowers are also highly popular with bees - these markings draw the bees into the flower.

8. If you have a small garden, use spires of foxgloves, verbascums, aconitums and hollyhocks as these provide weeks of flower yet take up little ground space.

9. Try to plant a native hedge containing hawthorn - this native could theoretically attract 149 species of insect. These will sustain many British birds.

10. Make a pond, if you can do so safely - bear in mind that they are a hazard for young children.

Related: 6 tips for a wildlife-friendly garden.

The opinions expressed are those of the author and are not held by Saga unless specifically stated.

The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.